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A close-up photo of the common sunstar (Crossaster papposus), a starfish found in the North Atlantic and Pacific oceans. Photo: © Alexander Semenov

Invertebrates close-up never fail to please: with their bright colors and strange structures, they begin to take on patterns that are more art than animal.

So is true of this series of close-up photographs of starfish taken by researcher and photographer Alexander Semenov. But it isn’t enough to call them art: why are all those finger-like appendages waving around? And what are those bulbous spikes (or floral bouquets, if you’re feeling romantic)?

Lucky for us, two floors up from the Ocean Portal office sits Dr. Chris Mah, an expert on echinoderms (a group of ocean animals that includes starfish, sea urchins and brittle stars) at the Smithsonian National Museum of Natural History. He helped us to fill in some of the details.

Asterias rubens is the most common starfish found in the north-east Atlantic Ocean. Photo: © Alexander Semenov

The Worm-Like Soft Bits: The vast garden of waving worms isn’t a starfish experiment in cultivation, but how they breathe on the seafloor. Sea stars breathe passively, letting oxygen-rich seawater flow over those finger-like sacs, called papulae, which peek through the cracks in their protective plates. Like fish gills, papulae absorb the oxygen in seawater.

Solaster endeca is a yellow, orange, pink, purple or red seastar shaped like the Smithsonian logo. Here, its translucent yellow papulae filter oxygen from seawater. Photo: © Alexander Semenov

Such fleshy little fingers would make an excellent snack for a passing shrimp or another small predator. To defend themselves, starfish can retract their papulae to make them less obvious targets, as this Mithrodia clavigera, pictured below, has done.

The tropical nail-armed sea star (Mithrodia clavigera) has five long, spiky arms–up close, its papulae have retracted, leaving behind purple cups. Photo: © Alexander Semenov

The Bald, Grooved Patches: Starfish are powered by plumbing: a series of pipes carry food and oxygen through their bodies. Water pressure builds up in these pipes, which helps to support their bodies. It was long-thought that this water pressure also created suction, allowing starfish’s hundreds of tiny tube feet to attach to surfaces and slowly creep across the seafloor. But recent research has suggested that tube feet are more like sticky pads than suction cups.

How does water get in and out of this plumbing system? It goes through the sieve plate (also called a madreporite), a small bald patch on the starfish that, close up, looks like a tiny, grooved maze. While it’s not the only way that water can enter the plumbing, it’s a major intake valve for starfish.

Check out the madreporite on that Asterias amurensis! This starfish, native to Northern Japanese waters, invaded the colder waters of Australia in the 1990s and completely carpets the seafloor in some places. Photo: © Alexander Semenov

Most starfish only have one sieve plate, but larger ones with many arms can have far more. For example, the coral-devouring crown of thorns starfish can have up to 15 to power its many arms. And starfish that reproduce asexually by splitting their bodies in half sometimes end up with more than one.

Patiria pectinifera only has one sieve plate–the blue bald patch in the center right. Incidentally, in the center orange patch you can also spot the starfish’s white anus. Photo: © Alexander Semenov

The Spiked Clubs: Humans aren’t the only species that came up with the mace as weaponry. Instead of being offensive tools, starfish spines (as they’re known) protect them from the smothering force of mud and debris. It’s likely that they also protect against predators, but a starfish’s first line of defense is stinky and poisonous chemicals.

Crossaster papposus is speedy for a starfish–it can move more than 5 meters in 12 hours. Here, wafting papulae are interspersed by spiky spines. Photo: © Alexander Semenov

Not all starfish spines are spiky. These purple spines of Evasterias retifera (below) in a field of orange papulae are low and stubby with lovely white notches. Other species have more architectural spines shaped like pyramids or tall spires.

Evasterias retifera, found in cold, northern waters, has blunt purple spines among orange clusters of papulae. Photo: © Alexander Semenov

The Tiny, Bitey Mouths: A slow-moving lifestyle puts starfish in danger of becoming overgrown with algae or other encrusting organisms. As a defense, many starfish are speckled with small, extendable “claws” called pedicellariae, which you can see in the photo below. In some species, the pedicellariae surround the spines and, if the starfish is threatened, will extend out to the spine’s full height! In other species, they are flat and spread out over the starfish’s skin. “They can look like a pair of lips or small jaws,” said Mah. “They probably look like monsters if you’re small enough to appreciate them.”

The tiny white bumps surrounding the larger white bumps (spines) on this Aphelasterias japonica are its pedicellariae. Photo: © Alexander Semenov

  Learn more about ocean invertebrates from the Smithsonian’s Ocean Portal.

The gooseneck barnacle (with a relaxed penis at arrow) is capable of a method of sex previously unobserved in barnacles, upending 150 years of theory. Image via Barazandeh, et al. Proc. R. Soc. B.

Barnacles are renowned for the size of their penises. The strange-looking creatures, which live inside shells glued to rocks or boat hulls, have outsized members that are among the longest in the animal kingdom relative to their size—their penises can stretch up to eight times their body length. Barnacles can even change the size and shape of their penis depending on the amount of wave action in their ocean real estate.

Perhaps this is why the sex lives of barnacles have long been of interest to scientists—luminaries such as Darwin, among others, closely studied the subject. Until recently, though, scientists recognized just two methods of reproduction in the species, and both left unanswered questions.

Pseudo-copulation, in which the penis enters a neighboring barnacle’s shell and deposits sperm, has been observed, but this method restricts them to reproducing only with others in their vicinity. Scientists have also observed that individual barnacles with no neighbors can reproduce, and they assumed this was accomplished through self-fertilization, because most barnacles are hermaphrodites.

Gooseneck barnacles (Pollicipes polymerus) taken at Limekiln Point on San Juan Island. Photo: Biriwilg, Wikimedia Commons

Now, though, researchers at the University of Alberta, Edmonton and Bamfield Marine Sciences Centre in British Columbia seem to have discovered a new reproduction method while studying the gooseneck barnacle (Pollicipes polymerus), upending more than 150 years of theory. Previously, the researchers had noticed that in other studies of the gooseneck barnacle, self-fertilization was never observed. They also saw sperm leaking from the barnacles in the field, which made them consider the possibility that barnacles could pick up sperm from the water.

In the study, the scientists collected gooseneck barnacles—both isolated and in pairs—along with their fertilized eggs from Barkley Sound in British Columbia to take back to the lab so they could genetically analyze the paternal combinations. The DNA of the fertilized eggs revealed that none of the isolated barnacles had produced embryos through self-fertilization—so one hundred percent of these eggs must have been fertilized by capturing sperm from the water.

Surprisingly, though, even some of the barnacles that resided in pairs had embryos that had been fertilized with sperm from a non-neighbor. This left one possibility: that the barnacles release their sperm into the ocean and let the water carry it to distant neighbors. This type of fertilization has been observed in other marine animals that can’t or don’t move, but it was always assumed that barnacles can’t reproduce in this way.

The authors point out that this mode of reproduction may be unusually common in this particular barnacle species because of the small size of their penis—but the fact that this phenomenon occurs at all opens the door to re-thinking the biology of these creatures. Other barnacle species might also have more mating options, with fathers coming from farther afield than previously thought.

 Learn more about the ocean from the Smithsonian’s Ocean Portal. 

Small red boring sponges embedded in star coral, killing the coral polyps immediately surrounding them. Image via Sean Nash, Flickr

Whenever anyone talks about ocean acidification, they discuss vanishing corals and other shelled organisms. But these aren’t the only organisms affected—the organisms that interact with these vulnerable species will also change along with them.

These changes won’t necessarily be for the good of the shell and skeleton builders. New research published in Marine Biology shows that boring sponges eroded scallop shells twice as fast under the more acidic conditions projected for the year 2100. This makes bad news for the scallops even worse: not only will they have to cope with weakened shells from acidification alone, but their shells will crumble even more quickly after their cohabiters move in.

Boring sponges aren’t named thus because they’re mundane; rather, they make their homes by boring holes into the calcium carbonate shells and skeletons of animals like scallops, oysters and corals. Using chemicals, they etch into the shell and then mechanically wash away the tiny shell chips, slowly spreading holes within the skeleton or shell and sometimes across its surface. Eventually, these holes and tunnels can kill their host, but the sponge will continue to live there until the entire shell has eroded away.

Alan Duckworth of the Australian Institute of Marine Science and Bradley Peterson of Stony Brook University in New York brought boring sponges (Cliona celata) and scallops (Argopecten irradians) into the lab to examine the effects of temperature and acidity (measured through pH) on drilling behavior. They set up a series of saltwater tanks to compare how much damage sponges did to scallops under current temperature and ocean conditions (26°C and pH 8.1), projected conditions for 2100 (31°C and pH 7.8), and each 2100 treatment alone (31°C or pH 7.8).

Cliona celata (yellow), the boring sponge species used in the study, is commonly found on oysters and scallops and lives throughout the Atlantic and Mediterranean. Here, numerous sponges have drilled into coral. Image via Bernard Picton, National Museums Northern Ireland

Under higher acidity (lower pH), boring sponges drilled into scallop shells twice as fast, boring twice as many holes and removing twice as much shell over the course of the 133-day study. The lower pH alone weakened the shells, but after the boring sponges did their work, the scallop shells were an additional 28% weaker, making them more vulnerable to predation and collapse from the sponges’ structural damage.

The sponges weren’t entirely thrilled by the water’s higher acidity, which killed 20% of the them (although the researchers aren’t sure why). Despite this loss, 80% of the sponges doing twice as much drilling meant more damage to shelled organisms in total. Temperature did not affect sponge behavior at all.

This study illustrates a classic positive feedback loop, where weakness in the shells leads to more weakness. And not through the sponge-drilled holes alone: the addition of sponge-drilled holes creates more surface area for acidification to further erode the shells, hastening each scallop’s inevitable collapse. It’s tempting to speculate out to the rest of the system—that the sponges are destroying their own habitat more quickly than scallops can produce it—but we don’t really know whether in the long run this is also bad news for the sponges.

Though a small and specific example, this study illustrates how a seemingly small change—more acid and weaker shells—can ripple out and affect other organisms and the rest of the ecosystem.

  Learn more about coral reefs from the Smithsonian’s Ocean Portal.

2012 was a big year for squid science. Photo Credit: © Brian Skerry, www.brianskerry.com

Despite covering 70 percent of the earth’s surface, the ocean doesn’t often make it into the news. But when it does, it makes quite a splash (so to speak). Here are the top ten ocean stories we couldn’t stop talking about this year, in no particular order. Add your own in the comments!

2012: The Year of the Squid From the giant squid’s giant eyes (the better to see predatory sperm whales, my dear), to the vampire squid’s eerie diet of remains and feces, the strange adaptations and behavior of these cephalopods amazed us all year. Scientists found a deep-sea squid that dismembers its own glowing arm to distract predators and make a daring escape. But fascinating findings weren’t relegated to the deep: at the surface, some squids will rocket themselves above the waves to fly long distances at top speeds.

James Cameron Explores the Deep Sea Filmmaker James Cameron has never shied away from marine movie plots (See: Titanic, The Abyss), but this year he showed he was truly fearless, becoming the first person to hit the deepest point on the seafloor (35,804 feet) in a solo submarine. While he only managed to bring up a single mud sample from the deepest region, he found thriving biodiversity in the other deep-sea areas his expedition explored, including giant versions of organisms found in shallow water.

Small fish, such as these schooling sardines, received well-deserved attention for being an important part of the food chain in 2012. Photo Credit: © Erwin Poliakoff, Flickr

Small Fish Make a Big Impact Forage fish—small, schooling fish that are gulped down by predators—should be left in the ocean for larger fish, marine mammals and birds to eat, according to an April report from the Lenfest Forage Fish Task Force. These tiny fish, including anchovies, menhaden, herring and sardines, make up 37% of the world’s catch, but only 10% are consumed by people, with the rest processed into food for farmed fish and livestock. With the evidence mounting that forage fish are worth more as wild fish food, state governments and regional fishery management councils are making moves to protect them from overfishing.

Marine Debris and Plastic Get Around In June, a dock encrusted with barnacles, sea stars, crabs and other sea life washed ashore on the coast of Oregon. It had floated across the Pacific from a Japanese port more than 5,000 miles away—a small piece of the estimated 1.5 million tons of marine debris set afloat by the 2011 Tohoku tsunami. But that’s not the only trash in the sea. Researchers found ten times as much plastic in the “pristine” Antarctic oceans than they expected. Some species are even learning to adapt to the ubiquitous ocean plastic.

These tropical tangs and their coral reef habitat are protected at Hawaii’s Papahanaumokuakea Marine National Monument. Photo Credit: Claire Fackler, CINMS, NOAA, Flickr

Taking Measure of Coral Reef Health Australia’s iconic Great Barrier Reef, so large it can be seen from space, is not doing well. An October study found that since 1986, half of the living coral has died because of warming water, predation and storm damage. And it’s not just Australia: the December Healthy Reefs report gave most Mesoamerican reefs a “poor” rating. It’s hard to escape that gloom, but there were glimmers of hope. Some coral species proved able to adapt to warmer water, and changing circulation caused by the warming ocean may create refuges for coral reef habitat.

Shark Finning Slowing Down? The fishing practice of shark finning—slicing off a shark’s fins before tossing it back in the ocean to slowly sink and suffocate—began its own slow death in 2012. A steady stream of U.S. states have banned the sale of shark finsning; the European Union will now require fisherman to land sharks with their fins on; four shark sanctuaries were created in American Samoa, the Cook Islands, Kosrae and French Polynesia; and, in July, China announced that official banquets would be prohibited from serving shark fin soup (although the ban may take up to three years to go into effect).

Arctic ice reached an all-time low in 2012. Photo Credit: NASA/Kathryn Hansen

Arctic Sea Ice Hits All-Time Low On September 16, sea ice extent reached a record low in the Arctic, stretching 3.41 million square kilometers—that’s 49% lower than the 1979-2000 average minimum of 6.7 million square kilometers. What’s more, its melt rate is increasing: 2012 had the largest summer ice loss by more than one million square kilometers. This change is expected to affect ecosystems—from polar bears to phytoplankton—and accelerate warming in the area, eventually melting Greenland’s ice sheet and raising sea level dramatically.

Hurricane Sandy Elevates Awareness of Sea-Level Rise This year certainly opened our eyes to the severity of climate change and sea-level rise. The east coast of the U.S., where scientists project sea-level will rise three to four times faster than the global average, got a glimpse of its effects when Hurricane Sandy caused $65 billion in damage, took at least 253 lives, and flooded Manhattan’s subways in October. The disaster inspired The Economist, Bloomberg Businessweek and other major news sources to take a closer look at climate change and what it means for us all.

Using satellite photos, researchers counted twice as many emperor penguins living in Antarctica than they thought existed. Photo Credit: Martha de Jong-Lantink, Flickr

Counting Ocean Animals from Space Scientists took advantage of satellite technology this year to learn more about ocean wildlife. The first satellite-driven census of an animal population discovered that there are twice as many emperor penguins in Antarctica as previously thought, including seven new colonies of the large flightless birds. A second study tracked the travels of sea turtles by satellite, which could help researchers get a better idea of where they might interact with fisheries and accidentally end up caught in a net.

The Ocean Gets a Grade The first tool to comprehensively assess ocean health was announced in August 2012—and the ocean as a whole received a score of 60 out of a possible 100. This tool, the Ocean Health Index, is novel in that it considered ten ways the ocean supports people, including economies, biodiversity, and recreation. The U.S. scored a 63, ranking 26th globally, while the uninhabited Jarvis Island took home an 86, the top grade of the 171 rated countries.

–Hannah Waters, Emily Frost and Amanda Feuerstein co-wrote this post

  Learn more about the ocean from the Smithsonian’s Ocean Portal.

Photo by Nick Hobgood

During the holiday season, even the ocean gets in the spirit! The Christmas tree worm (Spirobranchus giganteus) is a type of polychaete, a group of segmented worms mostly found in the ocean. It lives on tropical coral reefs and resembles a fluffy fir tree adorned with colored ornaments. Each worm has two tree-like appendages that are used to breathe and to catch meals of plankton floating by.

The Christmas tree worms are sedentary, attaching themselves to coral cover that act as their home base. Once attached, they create a calcium carbonate tube that they can then retract into for protection. The fluffy, eye-catching section of the worms that attract divers are small in size, usually not bigger than a few inches, but the remainder of the worm (hiding in its burrow) can be almost twice that size.

Check out more holiday-themed ocean animals and phenomena on the Ocean Portal! 

Photo by Nick Hobgood

A colorful “forest” of Christmas tree worms. Photo by Nick Hobgood

Read more articles about the holidays in our Smithsonian Holiday Guide here

 Learn more about the ocean from the Smithsonian’s Ocean Portal.